The present disclosure relates, in various exemplary embodiments, to toner compositions and processes for producing the same. The present disclosure also relates to dry-powder electrophoretic displays employing such toner compositions.
Photo-electrophoretic imaging systems and electrophoretic displays are known in the art. Electrophoretic imaging systems and displays generally include electrically photosensitive pigment particles dispersed in a carrier liquid, or suspending fluid, and arranged between two parallel and generally transparent conducting electrode panels.
Conventional electrophoretic display systems are typically one of two types, namely, a one particle system or a two particle system. In a one particle system, the suspending fluid is colored with a dye. In a two particle system, two types of particles of different colors and opposite charge are dispersed in a clear fluid. Particles acquire their charge via the adsorption of polymeric charge control agents (CCAs) that are added to the fluid. Under the influence of an electric field, the charged particles migrate towards the oppositely charged electrode.
The particles are typically prepared using a liquid toner process to create composite particles consisting of a pigment and a resin. The particles generally range from about 1 to about 10 micrometers in size. The resin used includes thermoplastics such as a poly(ethylene-co-vinyl acetate) or a poly(ethylene-co-methacrylic acid). The particles are then encapsulated in a microcapsule or a photopolymer structure to produce a display device.
Electrophoretic displays using these liquid systems, however, have a number of drawbacks. In unencapsulated systems, for example, articles that make up the system tend to cluster and settle, which reduces the performance and the life of the electrophoretic display. Encapsulated systems also experience performance problems over time. For example, above 60° C., the polymer becomes soft and sticky, which leads to particle agglomeration and overall degradation in device performance. These problems limit the robustness of the materials packaging, and preclude any device preparation steps, such as hot lamination. Additionally, the desorption of charge control agents from the particles in the solution leads to decay of the electrophoretic mobility of the particles.
As an alternative to conventional electrophoretic displays utilizing liquid systems, there is a growing interest in dry-powder electrophoretic displays. Dry-powder electrophoretic displays as used herein refers to electrophoretic displays wherein the toner particles are not dispersed in a suspending fluid or encapsulated as is understood in the art. Dry-power electrophoretic displays offer advantages over conventional liquid electrophoretic systems. An important aspect is that the solventless nature of the dry-powder display greatly reduces the loss of particle charge over time. Additionally, known dry-powder electrophoretic displays are typically limited by the size of the toner particles, i.e., up to about 50 micrometers, employed in such systems. The use of large toner particles, however, often results in poor image quality and visual graininess.
It is therefore desirable to provide a new dry-powder electrophoretic display system. It is further desirable to provide toner compositions and particles suitable for use in such a system.